Contact lenses which yield a cosmetic effect, i.e., a change in the visual appearance of the wearer's eye, are well known and have been available commercially for many years. The principal object of many of these lenses is to improve the color of the iris or its texture. The appearance of an iris is relatively complex, showing multiple colors and textures (collectively referred to herein simply as "color", as in a "colored contact lens"). See, for example, Jahnke, U.S. Pat. No. 5,414,477. The appearance of the natural iris is not a simple solid color, but a structure comprising many lines and different colors. Some cosmetic lens wearers prefer a colored contact lens that duplicates this natural complexity. For these wearers, the more natural their eyes appear with the lens, the more appealing they find the cosmetic effect of the lens. Other cosmetic contact lens wearers are interested in a more striking eye change, and the contact lens patterns and colors that these customers prefer may deviate from a common natural looking eye in order to make their eyes more distinct. The more a contact lens can duplicate this complexity, the more appealing it is considered to be as a consumer product.
Colored contact lenses are commonly made in two ways. One is by bonding, or entrapping, a dye to a lens, such as diazo, triazo, or vat dyes, which permeate the lens. This method is considered limiting because only non-opaque dyes can be used. The resulting contact lens will be colored, but the entire lens still transmits significant amounts of light through the part of the lens covering the iris. This tends to produce generally subtle color changes, which reduces the utility of the lens to effect a cosmetic change with dark colored eyes, for instance.
Opaque lenses may be produced using vat, diazo or triazo dyes by first soaking a hydrophilic lens in a BaCI solution, removing the lens from the BaCI solution, soaking the lens in an H.sub.2 SO.sub.4 solution so that the barium precipitates with the sulfate ion to form BaSO.sub.4. Thereafter, the application of the vat, diazo or triazo dyes can produce an opaque color. This process, however, is extremely time consuming, involves many steps, and is difficult to scale.
The other common method for making a colored contact lens is by printing an ink-containing pigment (or pigments) to the surface of the lens. This can be by printing the ink directly on the surface of the lens, or on a casting cup which then transfers the printing to the lens. Printing is also considered somewhat limited due to the types of pigments that have been used to date. These pigments absorb and reflect light to give a cosmetic effect. Texture, for instance, is achieved by choosing the pattern(s) in which the ink is applied to the lens surface, and the number of ink colors applied. Current technology relies upon pigments that have limited or no characteristics other than direct absorption or reflection of light. There has been a continuing effort in the industry to improve colored contact lenses by printing pigments on the lens that give the cosmetic appearance that many consumers want, and attempting to achieve cosmetic effects that may have appeal such as a perception of depth, and unusual textural effects.